This is a case of subarachnoid hemorrhage.  These typically present in the elderly with "thunderclap" headache and altered neurological status. The underlying cause is usually an arterial aneurysm which allows blood into the subarachnoid space irritating the brain linings.  Trauma is another cause.

CT is the best imaging modality to show acute bleeds and any major mass effect from them.

These patients require neurosurgical management or review, along with aggressive hydration and blood pressure control while preserving cerebral blood flow.

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Thanks to Dr David Cuete for originally uploading this case. The original can be viewed here.